Unable to use config_translation to translate top_label toc_type entity field

Problem/Motivation

On multilingual sites, you can't translate the top_label field of the configuration stored within a toc_filter config entity.

Steps to reproduce

• Install Drupal core, 10.4 || 11.x (its not specific to a particular version, these are the two I tested with)
• Enable toc_api_example and config_translation, eg. ddev drush en -y config_translation toc_api_example
• Add an additional language (/admin/config/regional/language/add)
• Create some content with some <h2>'s in the body field
• View the content in the alternate language
• At this point, we expect that the "Back to top" links will be in the default English and not translated. Lets go translate them!
• Go to Structure > Table of contents types. Click Translate from the Operations column next to Default
• Click Edit/Add from the Operations column for the language added in the previous step

Expected result

The "Back to top" (top_label) option should be available to translate.

Actual result

You can't translate the "Back to top" (top_label) option. You're stuck with "Back to top" in all languages.

Proposed resolution

The config schema declares this setting as a type string. It should be type label so that it can be translated into other languages using config_translation module.

Remaining tasks

MR